There is a number of known processes in which chemical reactions are initiated by means of catalysts in a fluidized bed, for example in oxychlorination, in which ethylene-oxygen and HCl are reacted in a fluidized-bed reactor over a copper-containing catalyst to give 1,2-dichloroethane and water.
In such fluidized-bed processes, abrasion of the fluidized-bed particles inevitably occurs, resulting in fine dust in the fluidized bed. Since these fine dust particles are entrained by the reaction gas mixture, they can be separated off inside or outside the reactor, for example by cyclones connected in series or by fine dust filters, for example by hoses of a Gore-Tex membrane on PTFE needle felt.
German Laid-open Specification 20 19 210 and also DE-40 30 086-C1 disclose fluidized-bed reactors and fluidized-bed processes, respectively, comprising filter cartridges, arranged inside the reactor, for the exit gas. Such filter cartridges invariably allow small amounts of fine dust to pass through (cf. expert opinion DE-21 66 912-A1, in particular the last paragraph of the description of this publication).
Owing to the physical circumstances of the fluidized beds used, cyclone inlets must be arranged at a certain minimum height above the fluidized bed since from this height onward the dust content in the gas taken off is approximately constant, and about 25% of the height of the reactor may be stated as an example without the invention being restricted to these dimensions.
It is known that efforts have been made to replace the cyclones and the downstream fine dust filters with a single fine dust filter arranged directly in the reactor, it being possible to clean the filter cartridges used by means of compressed gas pulses from the series side. The filters which are used may dip directly into the fluidized bed, which can inevitably lead to a reduction in the height of reactors. Furthermore, such a procedure should permit complete dust separation.
A particular disadvantage of this procedure is, however, that fine dust fractions which inevitably differ considerably from the desired spherical shape of the fluidized-bed particles inevitably accumulate in the fluidized bed, so that the characteristics of the fluidized bed change. While a very small amount is useful for better fluidization of the fluidized bed, larger amounts can lead to a transition from an effervescent fluidized bed to a percussive fluidized bed or to coating of the cooling surfaces, which leads to a gradual deterioration and finally to the collapse of heat transfer.